I have redeemed a Business-class ticket from SCL to TPE. However, when I checked in online, I was down-graded from business class to the coach class. I tried to call Delta, but they said there was a flight change. As a matter of face, nothing has changed since all my itinerary remained the same. What can I do? I actually purchased the ticket like a year ago because I was afraid they ran out of seats. Now, I have got a purchased ticket, but they down-graded me with the system excuse. Please help!